The present invention generally relates to library producing methods used in measuring sectional shapes of patterns that have periodic uneven structure by using light, and more concretely to library producing methods used in measuring sectional shapes of fine periodic patterns (such as line & space patterns) formed on wafers that are used for device fabricating processes, wherein the devices (for example, semiconductor devices such as ICs or LSIs, imaging devices such as CCDs, display devices such as liquid crystal panels, or detecting devices such as magnetic heads) are fabricated by exposing wafers as photosensitive substrates.
Along with recent demands for higher integration of semiconductor devices such as ICs or LSIs, fine processing technology for semiconductor devices has been greatly improved. As exposure apparatuses to which the fine processing technology is applied, many kinds of reduction projection exposure apparatuses (steppers) are proposed that form an image of a circuit pattern on a mask (reticle) as an original exposure form to a wafer as a photosensitive substrate, and exposing the photosensitive substrate by a step-and-repeat method.
Generally, it is important to decide exposure conditions such as the exposure dose on a wafer or the focusing position (position along the optical axis of the projection optical system) of the wafer appropriately in exposing a fine circuit pattern by using a stepper that has a projection optical system. Therefore, a conventional exposure apparatus decides an optimum exposure condition by developing the photosensitive substrate (wafer) and by measuring the critical dimension of the circuit pattern on the wafer by using a light microscope or a critical dimension measuring apparatus after exposing the pattern onto the wafer by changing the exposure condition (i.e., at least each one of the exposure doses (shutter opening time) or a focus position) per 1 shot, each in a test exposure process (send ahead process) before the mass production process.
For example, the shot area (the exposure area) is exposed with its focus maintained as a constant and its exposure dose (shutter opening time) changed constantly per 1 shot in a crosswise arrangement, with its exposure dose maintained as a constant, and its focus changed constantly per 1 shot in a lengthwise arrangement. Then, the critical dimension of the line and space resist pattern (hereinafter called the L&S pattern) formed in each shot is measured by using a scanning electron microscope (SEM) after developing, the optimum focus position, and the optimum exposure dose of the projection lens is calculated.
Another method besides measuring the critical dimension by SEM is proposed in references 1 and 2. The method disclosed in these references shows the emission of polarized lights (the S polarized light and the P polarized light) onto a periodic pattern in order to measure the critical dimension. The disclosed method also shows the measure of a reflected light's conditions (intensity and phase) from the periodic pattern, detection of the change of the polarized light's conditions reflecting on the periodic pattern, and the calculation of the critical dimension of the periodic pattern in accordance with the change.
In references 3 and 4, inventors of the present invention proposed a method for obtaining the optimum focus position and the optimum exposure dose of the exposure apparatus in an exposing process by emitting the polarized light (the S polarized light and the P polarized light) to the periodic pattern, and measuring the critical dimension of the periodic pattern exposed onto the wafer in accordance with the conditions (intensity and phase) of the reflection light from the periodic pattern.
Sectional shape measuring apparatuses manufactured by several measurement hardware manufacturers (Accent Optical Technologies Corp., KLA—Tencor Corp., Nanometrics Corp., Nova Measuring Instruments Corp., Therma—Wave Corp., and Timbre Technologies Corp.) can measure the sectional shape of the periodic pattern by emitting the polarized light onto the periodic pattern, and comparing the measured value and calculated value of the condition change (intensity change and phase change) of the light reflected from the periodic pattern. The calculated value of the reflected light's condition change is calculated by using pre-determined periodic pattern shape and the optical constant (for example, a refraction index n or an absorption coefficient k) of the material that forms the periodic pattern as parameters, etc.
Reference 1; Japanese Patent Application Publication No. 11-211421
Reference 2; Japanese Patent Application Publication No. 11-211422
Reference 3; Japanese Patent Application Publication No. 9-36037
Reference 4; Japanese Patent Application Publication No. 10-22205
However, in order to measure and observe the periodic pattern using a SEM, it is necessary to cut the periodic pattern in a specific size as a sample, and to install the sample in a vacuum chamber, which takes much time and effort. In the case that the periodic pattern to be measured is formed by a chemically amplified resist, the measurement of the critical dimension will be inaccurate because the periodic pattern deforms by charging electrons when irradiating the periodic pattern with an electron beam for the measurement.
There is another problem in using the previously explained sectional shape measurement apparatus for measuring the sectional shape of the periodic pattern by emitting the polarized light to the periodic pattern and comparing the measured value and the calculated value of the condition change (intensity change and phase change) of the light reflected from the periodic pattern. The measurement of the critical dimension will be inaccurate when an actual optical constant of the material (the object) which forms the periodic pattern is different from a calculated optical constant of the material which forms the periodic pattern used in calculating the condition change of the reflected light, because of aged deterioration or dispersion among the lots.